Biology Reference
In-Depth Information
reason, the year 2008 was officially announced
as the International Year of the Potato by the
Director-General of FAO (
http://www.fao.org/
Potato as a vegetatively propagated crop is
more exposed to disease not only through attacks
of pathogens during vegetation season, but also
through the transmission of pathogens to the next
generation by infected seed tubers.
Late blight, today the most important potato
disease worldwide, is caused by
Phytophthora
infestans
(Mont.) de Bary. This disease affects
potato foliage and tubers. Total destruction of
potato crops occurred in 1845 and 1846 and
it was distastrous. The decimation of the basic
food crop in Ireland caused the death of one
million people and emigration of another mil-
lion, in what is known as the Irish Potato Famine
(Bourke 1991). Until now, the problem of late
blight control has not been solved through use of
the genetic resistance of the host plant. Despite
more than 100 years of concerted efforts world-
wide toward breeding resistant potato varieties
and, in recent decades, releasing efficiently resis-
tant cultivars, chemical control is still the pre-
dominant method employed to protect the potato
crop. Current management practices rely on
multiple fungicide applications for disease con-
trol (up to15 sprays per season, as in the U.S.
state of Maine), a practice that is harmful to
the environment and to people (Schepers and
Spits 2006; Forbes 2009). Accordingly efforts
are being directed toward improving preventive
control strategies by reducing doses or reduc-
ing the number of protective fungicide sprays
on more resistant potato cultivars (Kessel et al.
2006; Spits et al. 2007).
In 1999 annual losses in global potato pro-
duction caused by late blight were estimated at a
cost of US$3 billion by Duncan (1999). Ten years
later Haverkort and colleagues (2008) estimated
the annual losses caused by late blight in Euro-
pean Union countries, attributable to the cost of
crop damage and chemical control, at
countries was estimated at
6 billion. The same
authors assessed the global cost of losses caused
by late blight, assuming global potato produc-
tion on 20 Mha with an average yield of 16 T/ha.
They calculated M
€
4,800 as a very conservative
loss annually caused by late blight.
Effective solution of the late blight problem
in potato production by utilization of resistant
cultivars would efficiently increase income and
food security on a world scale.
€
History of Late Blight Resistance
Breeding
In modern potato breeding programs, resistance
to late blight was and still is an important issue. In
the nineteenth century potato cultivars selected
within
S. tuberosum
sources varied in suscep-
tibility to late blight. In this period, instead of
several popular cultivars, there were hundreds
of them in cultivation, but of very local impor-
tance (Toxopeus 1964). It was noted during the
potato famine in the 1840s, that a few of the
cultivars grown in Europe exhibited some resis-
tance while other cultivars were totally damaged
(Glendinning 1983). However,
S. tuberosum
was
not a sufficient source of resistance variation for
selection of highly resistant cultivars.
Thus, in the beginning of the twentieth cen-
tury the resistant Mexican species
S. demissum
and
S. stoloniferum
were introduced in breed-
ing for resistance to late blight (Salaman 1937).
Since the discovery around 1920 of the hyper-
sensitive reaction of
S. demissum
to
P. infes-
tans
, attempts have been made to transfer the
R genes responsible for this type of resistance
into
S. tuberosum
by backcrossing
S. demissum
with potato cultivars (Toxopeus 1956). Breeding
centers in the USA, England, the Netherlands,
Germany, and Russia were actively engaged in
enhancing late blight resistance in bred culti-
vars. Soon it was found that this resistance in
new cultivars having single R genes was not sta-
ble and was overcome by new virulent races of
P. infestans
(Muller and Black 1952). At this
time breeders had recognized four completely
1 bil-
lion, while the value of potato production in EU
€
Search WWH ::
Custom Search